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Crustal thickness (H) and Vp / Vs ratio (κ) are two important parameters in characterizing a crustal structure. Their estimates from receiver function data often have large uncertainties due to the severe trade-off between the two parameters when the receiver functions only have the Moho P -to- S converted phase and its crustal multiples are weak or missing, which are common in tectonically active regions. Here, we extended the H –κ stacking method by combining receiver functions and PmP traveltimes to determine H, κ and Vp simultaneously. We developed a deconvolution technique to measure PmP traveltimes using the post-critical Moho P -wave reflection SsPmp in the teleseismic S wave. Synthetic tests show that the new methods can reliably extract the PmP traveltimes and determine crustal thickness and velocities as long as the Moho Ps is clear in receiver functions. We applied the methods to 63 broad-band seismic stations in the western Hubei Province of China. The results confirm the rapid increase of crustal thickness revealed in a previous study from the low-elevation plains in the eastern part of the study area to the mountains in the west. The corresponding increase of crustal Poisson's ratio from low-to-intermediate values to intermediate-to-high values suggests that the crust in the eastern part is more felsic, most likely due to delamination of a portion of the mafic lower crust of the Yangtze platform in the Late Mesozoic. [ABSTRACT FROM AUTHOR]

We decompose a general seismic potency tensor into isotropic tensor, double-couple tensor and compensated linear vector dipole using the eigenvectors and eigenvalues of the full tensor. Two dimensionless parameters are used to quantify the size of the isotropic and compensated linear vector dipole components. The parameters have well-defined finite ranges and are suited for non-linear inversions of source tensors from seismic waveform data. The decomposition and parametrization for the potency tensor are used to obtain corresponding results for a general seismic moment tensor. The relations between different parameters of the potency and moment tensors in isotropic media are derived. We also discuss appropriate specification of the relative size of different source components in inversions of seismic data. [ABSTRACT FROM AUTHOR]

Abstract: The Chaochou Fault, a major geological boundary in southern Taiwan is considered to be a part of the convergent plate boundary between the Eurasia Plate and the Philippine Sea Plate. We applied the Common Conversion Point stacking technique to teleseismic radial receiver functions and obtained Moho variation and crustal structure across the Chaochou Fault. In the Eurasia Plate to its west, the Moho depth is about 37km and the crust is subducting to the east beneath the Philippine Sea Plate with a dip angle of about 30° between the Backbone Belt and the Tananao Schist. In the Philippine Sea Plate, the Moho depth is about 17km. The Longitudinal Valley marks the collision boundary between the Eurasia Plate and the Philippine Sea Plate. The results suggest that the depth extent of the Chaochou Fault is about 30–35km and the fault becomes a “shallow-angle” thrust fault at depth. The Common Conversion Point image also shows several bending interfaces of velocity contrast in the crust. We proposed a simple model to explain the Philippine Sea Plate and Eurasia Plate collision process and the observed crustal deformations. [Copyright &y& Elsevier]

• We developed a joint inversion method by combination of surface-wave dispersions, receiver functions, Ps and SsPmp travel times. • We obtained detailed three-dimensional Vs and Vp/Vs ratio models in the area. • A northeast-dipping low Vs zone is observed in the upper crust of the Dabashan orocline. • We proposed a tectonic model on formation of Dabashan orocline. The Dabashan orocline is a large thrust belt in central China. Determination of its high-resolution three-dimensional (3D) crustal shear-wave (S -wave) velocity structure can enhance our understanding of the intracontinental evolution of the South China plate and North China plate. In this study, we estimated the Rayleigh wave phase and group velocities at periods of 5–50 s, P -wave receiver functions, and Ps and SsPmp travel times from 63 permanent stations and 29 portable stations; we also constructed a 3D S -wave velocity model and crustal thickness and V p / V s ratio maps of the Dabashan orocline and adjacent areas. The crustal thickness and V p / V s ratio maps show prominent thick crust (50–55 km) and high V p / V s ratios (1.8–1.85), suggesting a mafic lower crust in the Dabashan orocline. The 3D S -wave velocity structure shows northeast-dipping low-velocity anomalies in the upper crust of the Dabashan orocline, and high velocities extended from near the surface to the lower crust in the Hannan-Micang and Shennong-Huangling domes, suggesting deep roots of the two domes. We propose that the two domes acted as rigid indenters and rotated clockwise together with the South China plate, penetrating into the Qinling-Dabie orogenic belt. Weak sediments in the upper crust of the Dabashan orocline were compressed and blocked by the two domes and the rigid Qinling-Dabie orogenic belt, resulting in vertical accretion of the sediments and crust and subsequent formation of the northeast-dipping low-velocity anomalies and the thick crust beneath the Dabashan orocline. [ABSTRACT FROM AUTHOR]

Abstract: We report the first application of the Cut and Paste (CAP) method to compute earthquake focal mechanisms in the Messina Straits area by waveform inversion of Pnl and surface wave segments. This application of CAP has furnished new knowledge about low-magnitude earthquake mechanics that will be useful for improved understanding of the local geodynamics. This is possible because the CAP inversion technique can be applied to small earthquakes, for which traditional moment tensor inversion methods are not appropriate and P-onset focal mechanisms in the study area fail because of a lack of sufficient observations. We estimate the focal mechanisms of 23 earthquakes with local magnitudes in the range of 3–4 occurring in the 2004–2008 time period, and recorded by the broadband stations of the Italian National Seismic Network and the Mediterranean Very Broadband Seismographic Network (MedNet) run by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The solutions show that normal faulting is the prevailing style of seismic deformation in the northern part of the study area while co-existence of normal faulting and strike-slip has been detected in the southern part. In the whole area of investigation the T-axes of focal mechanisms display a preferential northwest-southeast direction of extension. Combined with the findings of previous investigations, this improved database of focal mechanisms allows us to better detail the transitional area between the extensional domain related to subduction trench retreat (southern Calabria) and the compressional one associated with continental collision (western-central Sicily). The observed spatial change of seismic deformation regime offers new data to current seismotectonic and seismic hazard investigations in the area of Messina Straits where a magnitude 7.2 earthquake caused more than 60,000 casualties on 28 December 1908. [Copyright &y& Elsevier]